1. Field of the Invention
The invention relates to a method and an apparatus for the automatic determination of presetting values for the opening positions of inking zone setting elements, in particular ink blades of ink slides, of an inking unit of a press.
2. Description of the Related Art
During printing, a printing material is moved successively through a plurality of printing units of a press, as a rule a printing ink being applied to the printing material in each printing unit. During autotypical overprinting, as a rule the four scale colors black, magenta, cyan and yellow and, if necessary, special colors are printed, there being a separate printing unit and therefore inking unit for each of these printing inks. The inking unit of each printing unit has an ink metering device, the ink metering device having a number of inking zone setting elements corresponding to the number of inking zones. The inking zone setting elements are also designated ink slides or ink blades. Depending on the opening position of the inking zone setting elements, printing ink is applied to an ink fountain roll, which is also designated a ductor roll. The quantity of ink reaching the ductor roll per inking zone as a function of the inking zone setting elements is transferred by a distributor roll or film roll to an inking unit roll arranged downstream of the latter and is moved by further inking unit rolls in the direction of a forme cylinder or plate cylinder of the respective printing unit. What is known as a transfer cylinder or rubber-covered cylinder interacts with the forme cylinder and transfers the printing ink from the forme cylinder to the printing material.
The color configuration of a printed product to be printed, what is known as the subject, is defined in a prepress stage in the form of image data. Here, what are known as area coverage values are defined for all colors to be printed and therefore for all the inking units involved in the print. For each individual image point of each inking zone of an inking unit involved in the print, an area coverage value is predetermined, an average or zonal area coverage value of the respective inking zone resulting from the area coverage values of the individual image points of an inking zone. One particular difficulty which arises during printing then resides on presetting the inking zone setting elements of the inking units involved in the printing from the image data from the prepress stage in such a way that as far as possible the first printed product printed with this presetting comes as close as possible to the original from the prepress stage.
According to the prior art, when determining presetting values for the inking zone setting elements, the procedure is such that zonal area coverage values for the inking zones involved in the print are determined from an image data set from a prepress stage, and in that, furthermore, the presetting values for the inking zone setting elements are determined from these zonal area coverage values. The image data set from the prepress stage is in this case normally available in the PPF format or else in the JDF format, it being possible for the zonal area coverage values according to the prior art to be calculated from such image data sets. However, the problem here is that the image data set provided from the prepress stage does not represent or depict the printing region exactly. Instead, the region covered by the image data set is normally larger than the region actually printing, since the image data set also depicts measurement control strips, for example, beside the actual printing region. In addition, the image data from the image data set from the prepress stage can be rotated and/or mirrored or inverted. Apparatus known from the prior art for determining presetting values for the inking zone setting elements have setting possibilities in order, for example, to mask out regions of the image data set outside the actual printing region, or to take into account the rotation and/or the mirroring of the image data of the image data set.
In this case, however, the determination of the actual printing region from the image data set from the prepress stage, and also the determination of the mirroring and/or rotation of the same, presents considerable difficulties, so that, according to the prior art, as a rule erroneous settings are made, on the basis of which incorrect zonal area coverage values and therefore ultimately incorrect presetting values for the inking zone setting elements are determined. Too much or too little printing ink is then supplied to the inking zones of inking unit, which necessarily leads to undesired color shifts and lightness shifts in the print and, as a result, to rejects. This is disadvantageous for cost reasons.